Multi-pass and multi-slab folded microchannel heat exchanger

ABSTRACT

A heat exchanger is provided including a first manifold and a second manifold separated from one another. A plurality of tube segments arranged in a spaced parallel relationship fluidly couple the first and second manifold. The plurality of tube segments includes a bend defining a first slab and a second slab. The second slab is arranged at an angle to the first slab. The heat exchanger has a multi-pass configuration relative to an air flow including at least a first pass and a second pass. The first pass has a first flow orientation and the second pass has a second flow orientation. The second flow orientation is different from the first flow orientation.

BACKGROUND

This invention relates generally to heat pump and refrigerationapplications and, more particularly, to a microchannel heat exchangerconfigured for use in a heat pump or refrigeration system.

Heating, ventilation, air conditioning and refrigeration (HVAC&R)systems include heat exchangers to reject or accept heat between therefrigerant circulating within the system and surroundings. One type ofheat exchanger that has become increasingly popular due to itscompactness, lower weight, structural rigidity, and superiorperformance, is a microchannel or minichannel heat exchanger. Ascompared to conventional plate-and-fin heat exchangers, microchannelheat exchangers are also more environmentally friendly as they utilizeless refrigerant charge which typically are synthetic fluids with highGWP (global warming potential). A microchannel heat exchanger includestwo or more containment forms, such as tubes, through which a cooling orheating fluid (i.e. refrigerant or a glycol solution) is circulated. Thetubes typically have a flattened cross-section and multiple parallelflow channels. Fins are typically arranged to extend between the tubesto augment efficient exchange of thermal energy between theheating/cooling fluid and the surrounding environment. The fins have acorrugated pattern, incorporate louvers to further enhance heattransfer, and are typically secured to the tubes via controlledatmosphere brazing.

In the heat pump and refrigeration applications, when the microchannelheat exchanger is utilized as an evaporator, moisture present in theairflow provided to the heat exchanger for cooling may condense and thenfreeze on the external heat exchanger surfaces. The ice or frost formedmay block the flow of air through the heat exchanger, thereby reducingthe efficiency and functionality of the heat exchanger and HVAC&Rsystem. Microchannel heat exchangers tend to freeze faster than theround tube and plate fin heat exchangers and therefore require morefrequent defrosts, reducing useful heat exchanger utilization time andoverall performance. Consequently, it is desirable to construct themicrochannel heat exchanger with improved frost tolerance and enhancedperformance.

SUMMARY OF THE INVENTION

According to one embodiment of the invention, a heat exchanger isprovided including a first manifold and a second manifold separated fromone another. A plurality of tube segments arranged in a spaced parallelrelationship fluidly couple the first and second manifold. The pluralityof tube segments includes a bend defining a first slab and a secondslab. The second slab is arranged at an angle to the first slab. Theheat exchanger has a multi-pass configuration relative to an air flowincluding at least a first pass and a second pass. The first pass has afirst flow orientation and the second pass has a second floworientation. The second flow orientation is different from the firstflow orientation.

In addition to one or more of the features described above, or as analternative, in further embodiments the first pass has a cross parallelflow orientation.

In addition to one or more of the features described above, or as analternative, in further embodiments the second pass has a cross counterflow orientation.

In addition to one or more of the features described above, or as analternative, in further embodiments a first portion of the plurality oftube segments forms the first pass and a second portion of the pluralityof tube segments forms the second pass.

In addition to one or more of the features described above, or as analternative, in further embodiments a number of tube segments arrangedwithin each of the first pass and the second pass is selected to reducethe formation of frost on the heat exchanger.

In addition to one or more of the features described above, or as analternative, in further embodiments the second portion has a greaternumber of tube segments than the first portion.

In addition to one or more of the features described above, or as analternative, in further embodiments a ratio of tube segments in thefirst portion to the second portion is 20:80.

In addition to one or more of the features described above, or as analternative, in further embodiments a ratio of tube segments in thefirst portion to the second portion is 40:60.

In addition to one or more of the features described above, or as analternative, in further embodiments a divider is arranged within thefirst manifold to define a first section and a second section. The firstsection is fluidly coupled to the first portion of the plurality of tubesegments, and the second section is fluidly coupled to the secondportion of the plurality of tube segments.

In addition to one or more of the features described above, or as analternative, in further embodiments a distributor is arranged within thefirst section of the first manifold.

In addition to one or more of the features described above, or as analternative, in further embodiments a distributor is provided betweenthe first pass and the second pass.

In addition to one or more of the features described above, or as analternative, in further embodiments the bend is formed about an axisarranged perpendicular to a longitudinal axis of the plurality of tubesegments.

In addition to one or more of the features described above, or as analternative, in further embodiments the bend of each tube segmentincludes a ribbon fold.

In addition to one or more of the features described above, or as analternative, in further embodiments wherein the angle between the secondslab and the first slab is about 180 degrees.

In addition to one or more of the features described above, or as analternative, in further embodiments each of the plurality of tubesegments is a microchannel tube having a plurality of discrete flowchannels formed therein.

A heat exchanger is provided including a first manifold and a secondmanifold separated from one another. A plurality of tube segmentsarranged in a spaced parallel relationship fluidly couple the first andsecond manifold. The plurality of tube segments includes a bend defininga first slab and a second slab. The second slab is arranged at an angleto the first slab. The heat exchanger has a multi-pass configurationrelative to an air flow including at least a first pass and a secondpass. An inlet of the heat exchanger and an outlet of the heat exchangerare both formed in the first slab.

In addition to one or more of the features described above, or as analternative, in further embodiments a first portion of the plurality oftube segments forms the first pass and a second portion of the pluralityof tube segments forms the second pass. The first portion has fewer tubesegments than the second portion.

In addition to one or more of the features described above, or as analternative, in further embodiments each of the plurality of tubesegments is a microchannel tube having a plurality of discrete flowchannels formed therein.

In addition to one or more of the features described above, or as analternative, in further embodiments a distributor is arranged adjacentan inlet of each pass of the heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of an example of a vapor refrigerationcycle of a refrigeration system;

FIG. 2 is a side view of a microchannel heat exchanger according to anembodiment of the invention prior to a bending operation;

FIG. 3 is a cross-sectional view of a tube segment of a microchannelheat exchanger according to an embodiment of the invention;

FIG. 4 is a perspective of a microchannel heat exchanger according to anembodiment of the invention;

FIG. 5 is a front view of a microchannel heat exchanger according toanother embodiment of the invention;

FIG. 6 is a side view of a microchannel heat exchanger according to anembodiment of the invention;

FIG. 7 is a perspective view of a microchannel heat exchanger accordingto yet an embodiment of the invention; and

FIG. 7a is a cross-sectional view of the microchannel heat exchanger ofFIG. 6 taken along line X-X according to yet an embodiment of theinvention; and

FIG. 7b is a cross-sectional view of the microchannel heat exchanger ofFIG. 6 taken along line Y-Y according to yet an embodiment of theinvention.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION

Referring now to FIG. 1, a vapor compression refrigerant cycle 20 of anair conditioning or refrigeration system is schematically illustrated.Exemplary air conditioning or refrigeration systems include, but are notlimited to, split, packaged, chiller, rooftop, supermarket, andtransport refrigeration systems for example. A refrigerant R isconfigured to circulate through the vapor compression cycle 20 such thatthe refrigerant R absorbs heat when evaporated at a low temperature andpressure and releases heat when condensed at a higher temperature andpressure.

Within this cycle 20, the refrigerant R flows in a counterclockwisedirection as indicated by the arrow. The compressor 22 receivesrefrigerant vapor from the evaporator 24 and compresses it to a highertemperature and pressure, with the relatively hot vapor then passing tothe condenser 26 where it is cooled and condensed to a liquid state by aheat exchange relationship with a cooling medium (not shown) such asair. The liquid refrigerant R then passes from the condenser 26 to anexpansion device 28, wherein the refrigerant R is expanded to a lowtemperature two-phase liquid/vapor state as it passes to the evaporator24. The low pressure vapor then returns to the compressor 22 where thecycle is repeated. The vapor compression cycle 20 described herein is aheat pump cycle operating in a heating mode. As a result, the outdoorcoil of the cycle 20 is configured as the evaporator 24 and the indoorcoil is configured as the condenser. When configured as a heat pump, thevapor compression cycle additionally includes a four-way valve 29disposed downstream of the compressor 22 with respect to the refrigerantflow that reverses the direction of refrigerant flow through the cycle20 to switch between the cooling and heating mode of operation. Itshould be understood that the refrigeration cycle 20 depicted in FIG. 1is a simplistic representation of an HVAC&R system, and manyenhancements and features known in the art may be included in theschematic.

Referring now to FIG. 2, an example of a heat exchanger 30 configuredfor use in the vapor compression system 20 is illustrated in moredetail. The heat exchanger 30 may be used as either a condenser 24 or anevaporator 28 in the vapor compression system 20. The heat exchanger 30includes at least a first manifold or header 32, a second manifold orheader 34 spaced apart from the first manifold 32, and a plurality oftube segments 36 extending in a spaced, parallel relationship betweenand connecting the first manifold 32 and the second manifold 34. In theillustrated, non-limiting embodiments, the first header 32 and thesecond header 34 are oriented generally horizontally and the heatexchange tube segments 36 extend generally vertically between the twoheaders 32, 34. However, other configurations, such as where the firstand second headers 32, 34 are arranged substantially vertically are alsowithin the scope of the invention.

Referring now to FIG. 3, an example of a cross-section of a heatexchange tube segment 36 is illustrated. The tube segment 36 includes aflattened microchannel heat exchange tube having a leading edge 40, atrailing edge 42, a first surface 44, and a second surface 46. Theleading edge 40 of each heat exchanger tube 36 is upstream of itsrespective trailing edge 42 with respect to an airflow A passing throughthe heat exchanger 36. The interior flow passage of each heat exchangetube segment 36 may be divided by interior walls into a plurality ofdiscrete flow channels 48 that extend over the length of the tubes 36from an inlet end to an outlet end and establish fluid communicationbetween the respective first and second manifolds 32, 34. The flowchannels 48 may have a circular cross-section, a rectangularcross-section, a trapezoidal cross-section, a triangular cross-section,or another non-circular cross-section. The heat exchange tubes 36including the discrete flow channels 48 may be formed using knowntechniques and materials, including, but not limited to, extruded orfolded.

The heat exchange tube segments 36 disclosed herein further include aplurality of fins 50. In one embodiment, the fins 50 are formed of asingle continuous strip of fin material tightly folded in a ribbon-likeserpentine fashion thereby providing a plurality of closely spaced finsthat extend generally orthogonal to the heat exchange tube segments 36.Heat exchange between the one or more fluids within the heat exchangetube segments 36 and an air flow, A, occurs through the outside surfaces44, 46 of the heat exchange tube segments 36 collectively forming aprimary heat exchange surface, and also through the heat exchangesurface of the fins 50, which forms a secondary heat exchange surface.

The heat exchanger 30 has a multi-pass configuration relative to airflowA, To achieve a multi-pass configuration, in one embodiment illustratedin FIGS. 4-6, the multi-pass configuration is achieved by forming atleast one bend 60 in each tube segment 36 of the heat exchanger 30. Thebend 60 is formed about an axis extending substantially perpendicular tothe longitudinal axis of the tube segments 36. In the illustratedembodiment, the bend 60 is a ribbon fold (see FIG. 6) formed by bendingand twisting the heat exchange tube segments 36 about a mandrel (notshown); however other types of bends are within the scope of theinvention. In one embodiment, a plurality of bends 60 may be formed atvarious locations along a length of the plurality of the heat exchangetube segments 36.

Bend 60 at least partially defines a first section 62 and a secondsection 64 of each of the plurality of tube segments 36, wherein in thebent configuration, the first section 62 forms a first slab 66 of theheat exchanger 30 relative to airflow A and the second section 64 formsa second slab 68 of the heat exchanger 30 relative to airflow A. In theillustrated, non-limiting embodiment, the bend 60 is formed at anapproximate midpoint of the tube segments 36 between the opposing firstand second manifolds 32, 34 such that the first and second sections 62,64 are generally equal in size. However, other embodiments where thefirst section 62 and the second section 64 are substantially differentin length are within the scope of the invention.

As shown in the FIGS. the heat exchanger 30 can be formed such that thefirst slab 66 is positioned at an obtuse angle with respect to thesecond slab 68. Alternatively, or in addition, the heat exchanger 30 canalso be formed such that the first slab 66 is arranged at either anacute angle or substantially parallel (FIG. 5) to the second slab 68. Asa result of the bend 60 between the first and second slabs 66, 68, theheat exchanger 30 may be formed having a conventional A-coil or V-coilshape. Forming the heat exchanger 30 by bending the tube segments 36results in a heat exchanger 30 having a reduced bending radius, such aswhen configured with a 180° bend for example. As a result, the heatexchanger 30 may be adapted to fit within the sizing envelopes definedby existing air conditioning and refrigeration systems.

Referring again to FIGS. 2, a plurality of first fins 50 a extend fromthe first slab 66 and a plurality of second fins 50 b extend from thesecond slab 68 of the heat exchanger 30. In embodiments where the heatexchanger 30 is formed by bending the plurality of tube segments 36. nofins are arranged within the bend portion 60 of each tube segment 36.The first fins 50 a and the second fins 50 b may be substantiallyidentical, or alternatively, may vary in one of size, shape, anddensity.

Conventional heat exchangers configured as evaporators of a heat pumptypically have a parallel flow configuration to achieve a desiredefficiency. However, parallel flow orientation leads to poor frosttolerance in microchannel heat exchangers. The heat exchanger 30 mayhave any of a variety of multi-pass configurations such that therefrigerant passes through the heat exchanger 30 in one or more of aparallel flow orientation, a cross flow orientation, and a counter floworientation for example. In one embodiment, a divider 38 may be arrangedwithin one or both of the first and second headers 32, 34 to increasethe number of passes, and therefore the length of the flow path, withinthe heat exchanger 30.

In the embodiment illustrated in FIG. 7, a divider 38 is arranged withinthe first header 32 to form a first section 32 a and a second section 32b. As a result, refrigerant supplied to an inlet (not shown) of thefirst header 32 is only configured to flow through the portion 36 a ofthe tube segments 36 fluidly connected to the first section 32 a. Afterpassing through a first portion 36 a of the tube segments 36, therefrigerant is received in the second header 34. Within the secondheader 34, the refrigerant flows away from the first portion 36 a oftube segments 36, towards a second, adjacent portion 36 b of tubesegments 36. The second portion 36 b may include the same number or adifferent number of tube segments 36 as the first portion 36 a. In oneembodiment, the ratio of tube segments in the first portion 36 a to thesecond portion 36 b is 20:80, or alternatively, 40:60.

The second header 34 may similarly include a divider 38 to define afluidly coupled first and second section 34 a, 34 b thereof. Therefrigerant is configured to flow from the second header 34 through thesecond portion 36 b of tube segments 36 fluidly connected to the secondsection 32 b of the first header 32 and to an outlet (not shown) formedtherein. Though the illustrated heat exchanger 30 includes two distinctportions of heat exchanger tube segments 36, heat exchangers 30 havingany number of portions of tube segments 36 that form discrete passesthrough the heat exchanger 30 are within the scope of the invention.

Evenly distributing refrigerant within a header, such as header 32 or 34or an intermediate header for example, is a common problem ofmicrochannel heat exchangers. It is generally easy to distribute therefrigerant evenly for small manifold lengths, but mal-distributionbecomes a more significant problem as the length of the manifoldincreases.

The heat exchanger 30 disclosed herein has improved refrigerantdistribution by partitioning at least one of the first and secondheaders 32, 34, with a divider 38. As a result, the lengths of themanifold in which refrigerant must be evenly distributed is decreased.In addition, by bending the heat exchanger 30, the need for anintermediate header, and therefore the distribution problems associatedwith such a header, is eliminated. In one embodiment, a longitudinallyelongated distributor insert 70, as is known in the art, may be arrangedwithin one or more of the sections of either the first header 32 or thesecond header 34 of the heat exchanger 30. The distributor insert 70 isarranged generally centrally within the interior volume of the headerand is configured to evenly distribute the flow of refrigerant betweenthe plurality of heat exchanger tubes 36 fluidly coupled thereto. In theillustrated, non-limiting embodiment, a first distributor insert 70 isarranged within the first section 32 a of the header 32. The distributorinsert 70 arranged within the first section 32 of the first header 30generally over a portion or the full length of the section 32 such thatthe refrigerant provided thereto will be more evenly distributed overthe length of the first section 32, thereby improving the heat transferof the heat exchanger 30. Alternatively, or in addition, anotherdistributor 70 may similarly be positioned within the second section 34b of the second header 34.

Because the direction of the air flow A is the same relative to thefirst and second portions 36 a, 36 b of the tube segments 36, therefrigerant within each of these portions has a differentflow-orientation. For example, in the illustrated, non-limitingembodiment, the air A flows from the first header 32 towards the secondheader 34. By supplying the refrigerant to an inlet of the first section32 a of the first header 32, refrigerant flowing through the firstportion 36 a of the tube segments 36, shown in detail in FIG, 7 a, has across-parallel flow orientation. In addition, the refrigerant flowingthrough the second portion 36 b of the tube segments 36. shown in moredetail in FIG. 7b , has a cross-counter flow orientation.

In conventional heat exchangers having a parallel flow configuration,two phase refrigerant enters the first section 32 with low-vapor qualitywherein it is configured to absorb heat from the air A and starts toboil. Because the boiling takes place at a constant temperature, thetemperature difference between the air and the refrigerant reducesprogressively as the air flows through the heat exchanger 30, reducingthe heat transfer that occurs, particularly in the downstream slab 68.This behavior reduces the overall effectiveness of the heat exchangerand also results in lower evaporating temperatures, which is detrimentalto both system efficiency and frost tolerance.

By dividing the plurality of heat exchange tube segments 36 of a heatexchanger 30 configured as an evaporator into a first portion 36 a and asecond portion 36 b to form two sequential passes, partially evaporatedrefrigerant is supplied from the first pass to the second pass. In thesecond pass, the refrigerant is fully boiled and the superheated vaporleaves the upstream face of the heat exchanger 30. By configuring thesecond pass to have a refrigerant flow cross-counter to the air flow A,the temperature difference between the air and the refrigerant is movefavorable. In addition, the presence of superheated vapor on theupstream face of the heat exchanger 30 prevents excessive frostaccumulation and improves frost tolerance.

A heat exchanger 30 having a multi-pass, multi-slab, folded constructionallows for optimization of the refrigerant pressure drop, therebyimproving performance. As the refrigerant flows through the heatexchange tube segments 36, the vapor quality continuously increases,leading to increased volumetric flow and therefore increased pressuredrop. By allocating progressively greater internal flow area as therefrigerant moves from one pass to the next, it is possible to greatlyimprove the pressure drop performance compared to conventional heatexchangers. Improvement in the operational efficiency of the heatexchanger 30 may allow the size of the heat exchanger 30 required for adesired application to be reduced. Alternatively, size of other systemcomponents, such as a compressor for example, may be reduced which inturn would cause even higher evaporation temperature and furtherreduction of defrost cycles as well as the system performance boost.

While the present invention has been particularly shown and describedwith reference to the exemplary embodiments as illustrated in thedrawing, it will be recognized by those skilled in the art that variousmodifications may be made without departing from the spirit and scope ofthe invention. Therefore, it is intended that the present disclosure notbe limited to the particular embodiment(s) disclosed as, but that thedisclosure will include all embodiments falling within the scope of theappended claims. In particular, similar principals and ratios may beextended to the rooftops applications and vertical package units.

1. A heat exchanger comprising: a first manifold; a second manifoldseparated from the first manifold; a plurality of tube segments arrangedin spaced parallel relationship and fluidly coupling the first manifoldand the second manifold, the plurality of tube segments including a benddefining a first slab and a second slab, the second slab being arrangedat an angle to the first slab; wherein the heat exchanger has amulti-pass configuration relative to an air flow including at least afirst pass and a second pass, the first pass having a first floworientation and the second pass having a second flow orientation, thesecond flow orientation being different than the first flow orientation.2. The heat exchanger according to claim 1, wherein the first pass has across parallel flow orientation.
 3. The heat exchanger according toclaim 2, wherein the second pass has a cross counter flow orientation.4. The heat exchanger according to claim 1, wherein a first portion ofthe plurality of tube segments forms the first pass and a second portionof the plurality of tube segments forms the second pass.
 5. The heatexchanger according to claim 4, wherein a number of tube segmentsarranged within each of the first pass and the second pass is selectedto reduce the formation of frost on the heat exchanger.
 6. The heatexchanger according to claim 4, wherein the second portion has a greaternumber of tube segments than the first portion.
 7. The heat exchangeraccording to claim 6, wherein a ratio of tube segments in the firstportion to the second portion is 20:80.
 8. The heat exchanger accordingto claim 6, wherein a ratio of tube segments in the first portion to thesecond portion is 40:60.
 9. The heat exchanger according to claim 4,wherein a divider is arranged within the first manifold to define afirst section and a second section, the first section being fluidlycoupled to the first portion of the plurality of tube segments, and thesecond section being fluidly coupled to the second portion of theplurality of tube segments.
 10. The heat exchanger according to claim 9,wherein a distributor is arranged within the first section of the firstmanifold.
 11. The heat exchanger according to claim 9, wherein adistributor is provided between the first pass and the second pass. 12.The heat exchanger according to claim 1, wherein the bend is formedabout an axis arranged perpendicular to a longitudinal axis of theplurality of tube segments.
 13. The heat exchanger according to claim 1,wherein the bend of each tube segment includes a ribbon fold.
 14. Theheat exchanger according to claim 1, wherein the angle between thesecond slab and the first slab is about 180 degrees.
 15. The heatexchanger according to claim 1, wherein each of the plurality of tubesegments is a microchannel tube having a plurality of discrete flowchannels formed therein.
 16. A heat exchanger comprising: a firstmanifold; a second manifold separated from the first manifold; aplurality of tube segments arranged in spaced parallel relationship andfluidly coupling the first manifold and the second manifold, theplurality of tube segments including a bend defining a first slab and asecond slab, the second slab being arranged at an angle to the firstslab; wherein the heat exchanger has a multi-pass configuration relativeto an air flow including at least a first pass and a second pass, aninlet of the heat exchanger and an outlet of the heat exchanger bothbeing formed in the first slab.
 17. The heat exchanger according toclaim 16, wherein a first portion of the plurality of tube segmentsforms the first pass and a second portion of the plurality of tubesegments forms the second pass, the first portion having fewer tubesegments than the second portion.
 18. The heat exchanger according toclaim 16, wherein each of the plurality of tube segments is amicrochannel tube having a plurality of discrete flow channels formedtherein.
 19. The heat exchanger according to claim 16, wherein adistributor is arranged adjacent an inlet of each pass of the heatexchanger.